The aim of this proposal is to gain a better understanding of the function of human knees with normal anterior cruciate ligaments (ACL), and ACL deficient as well as ACL grafts. Specifically, the in-situ load-deformation characteristics as well as the in-situ loads in the ACL will be determined under varus-valgus rotation, anterior-posterior translation, flexion-extension rotation and internal-external rotation of the knee. A kinematic linkage system will be used to measure the relative displacement of the bones when the specimens are subjected to these externally applied loads. Knowledge obtained from this study will be primary importance with respect to clinical treatment of ACL injury. Numerous surgical techniques and postoperative programs have been utilized to date in an effort to obtain better clinical results. However, no procedure has produced results that allow joint function to fully recover, and no graft has yet been designed which truly mimics the structural properties of the ACL. Success falls considerably short of normal knee function. It is our view that the favorable clinical results would not arrive without a better fundamental understanding of the structure and functional relationship of the ACL. In order to achieve the above objectives, a specifically designed six degree-of-freedom kinematic linkage system will be used to measure changes in the length of different ACL bundles during externally applied loads to an intact knee. These bundles will be isolated together with small bone blocks at each end. Tensile tests will be done to determine their load-deformation characteristics. The data will then be consolidated with the length measurements obtained from the intact knee tests so that the in-situ loads of the fiber bundles can be determined. A vector sum of these forces will be used to represent the loads of the entire ACL. A similar scheme will then be used to determine the ACL graft function (and joint kinematics) after reconstruction. The specific goals are to study effects of graft placement (anatomical position vs. "over-the-top") and the amount of graft pretension of joint motion.